Urinary tract infection among the increasing numbers of institutionalized elderly have received enhanced attention in the past few years. The epidemiology and importance of antibiotic resistance among urinary isolates of gram negative bacilli has only received minimal attention. Previous studies have mainly concentrated on outbreaks or epidemics of infection. We propose to study the endemic situation in a nursing home care unit. Preliminary data obtained from a prevalence study of a 100 bed Veterans Administration nursing home care unit indicates that approximately one-third of patients are colonized with multiply antibiotic resistant gram negative bacilli (GNB) and that 38% of the colonized patients acquired their organisms via cross- transmission. In an additional 14% of patients, transmission of R- plasmids between different GNB colonizing different patients could also be detected. The mode of transmission could not be definitively established in the prevalence survey, but geographic clustering suggested hand transmission as the predominant mechanism. The current proposal is to examine prospectively the prevalence, mode of acquisition of urinary colonization with Enterobacteriaceae bearing multiple resistance determinants, their associated R plasmids and risk factors for such acquisition over a two year period on the same nursing home unit.